This invention concerns means and methods for fuzing weapon projectiles, and more particularly, an improved projectile and fuzing system capable of detecting penetration of the projectile through various target layers of different properties.
It is well known in the art of weaponry to provide projectiles, as for example, artillery shells, mortar shells, rockets, bombs and other devices, with sensors or fuzes that detect target proximity or impact. The effectiveness of such projectiles can be dramatically improved if the fuzing system of the projectile is able to recognize the target in terms of its materials, thicknesses and numbers of layers, including voids. It is desirable to be able to program the projectile fuze to assess the materials and structure of the target as it penetrates so that the optimum delay and detonation time may be determined.
Proximity fuzes are extremely useful in determining when the projectile is approaching or about to strike a target. Where the fuzing strategy calls for the weapon to be detonated prior to impact, proximity detectors are extremely useful.
Where the fuzing strategy calls for the weapon projectile to be detonated on impact or a predetermined time after impact, accelerometers and timers (typically mounted in the base of the projectile) are frequently used to control detonation.
FIG. 1 shows a typical prior art projectile 10 having casing 12 powder charge 14 and base mounted accelerometer triggered fuze 16. FIG. 2, illustrates what happens when projectile 12 moving along path 13 strikes concrete wall 18 of thickness 20, thereby causing hole 22 to be created therein. In general, a large amount of debris 26 is ejected from wall 18 as projectile 12 exits.
FIG. 3 shows a typical accelerometer output as a function of time. Prior to impact, that is, prior to time T=0, accelerometer 16 has initial offset 28. As projectile strikes concrete wall 18, there is a rapid rise in accelerometer output as indicated by curve 30 to a maximum at 32 followed by a more gradual falloff at 34 to a further quiescent level 36 after projectile 12 has exited wall 18. In general, further quiescent level 36 is offset from initial level 18 by amount 38.
Vertical line 40 in FIG. 3 indicates the theoretical time required for projectile 12 to exit wall 18. It is often desired to use the output of accelerometer 16 to determine the exit time. However, as indicated by region 42 in FIG. 3, the time at which exit has occurred is difficult to accurately determine because of the lack of a sharp falloff transition in the accelerometer output and the large amounts of electrical noise that typically accompany such events. Thus, the inability to determine with precision and reliability the precise time at which a projectile makes a transition from one region of the target, (e.g. from a concrete layer into a further region of the target, as for example, a void or earthen layer) substantially interferes with efficient device fuzing. For example, in weapons designed to disrupt runways, it is extremely important to detonate the projectile after it has passed through the runway into the underlying gravel or other foundation layer and before it has penetrated deeply into the earth. When this is done correctly, a relatively small projectile is capable of producing a very large crater. If detonation is too early or too late, the extent of damage to the runway surface may be minor. Fixed timing intervals are unsatisfactory because they fail to accommodate varying initial layer thicknesses of a runway, bunker or other structure. A further problem with conventional prior art accelerometer-type fuzes is that they are highly susceptible to the very large shock waves which propagate or xe2x80x9cringxe2x80x9d back and forth from one end of the projectile to the other during the course of target penetration.
Accordingly, a continuing need exists for more accurate means and methods for determining when projectiles or probes go from one layer to another layer in a target so that different layers can be detected and, in the case of explosive projectiles, fuze detonation time delay accurately set. This need is especially important in connection with fuzes which are desired to penetrate through multiple target layers prior to detonation.
It is an advantage of the present invention that there is provided an improved means and method for detecting when a projectile is making a transition between target layers of different material properties. It is a further advantage of the present invention that one or more sensors are provided with the projectile whose output varies according to the nature of the material through which the projectile is penetrating.